A majority of states now have in effect traffic laws requiring headlights and taillights to be turned on when driving in the rain. In order to simplify drivers' compliance with such laws, a number of circuits have been designed which automatically turn on the headlights and taillights when the windshield wipers are turned on. U.S. Pat. Nos. 3,500,119, 3,519,837, 3,767,966, 3,600,596, 3,591,845, 4,057,742, 3,909,619, 4,097,839, and 3,824,405 disclose such devices. All of these devices have generally proved impractical because they are exceedingly expensive to manufacture, overly time consuming to install, unreliable in operation and/or cause inconvenience during use. For example, U.S. Pat. No. 3,500,119 issued to K. Price discloses an automatic headlight control system which uses three relays and must be connected to the headlight and taillight switches. The use of three relays adds considerable expense and complexity to the device, and the switch connections for most foreign and U.S. vehicles can require a number of hours of labor for installation.
The present invention overcomes the shortcomings of prior devices and includes a number of unique and advantageous features. The control system in accordance with the present invention may be easily installed entirely under the hood of any conventional motor vehicle to preexisting terminals and wires without any modifications thereof. The system includes a single relay circuit which, when installed, may be energized to provide electrical power directly to the low beam headlights and the taillights when the vehicle wiper motor is turned on while the vehicle engine is running. The system responds to the increased voltage generated across the windshield wipers by the vehicle's alternator when the engine is running and the windshield wipers are turned on. The system does not interfere with the high and low beam switches of the headlights or with the usual taillight switch. The invention may also be used in emergency vehicles to automatically turn on the low beam headlights when the vehicle's siren or emergency lights are turned on.
Many vehicles today are provided with window washers for cleaning windshield with the wipers and/or intermittent wiper action circuits for turning the wipers on intermittently in a very light rain or mist. Operation of either wiper device would cause prior devices such as is disclosed in Price to intermittently energize and deenergize the headlights and taillights.
This problem may also be overcome by the present invention. In one alternate embodiment of the invention, a delay circuit may be connected into the relay circuit so that the relay will not be energized by a single wipe of the windshield wiper blades, such as would result from operation of either the intermittent action of the wipers or of the window washer. In order to assure that the delay will be temperature independent a temperature sensitive resistive element such as a thermistor is inserted in the relay circuit across the windshield wiper motor.
In accordance with another alternative embodiment of the invention the low beams can be kept on while the vehicle is operating after the windshield wipers are turned off. This is accomplished by using a duel threshold relay and connecting the hot side of the ignition coil to the relay coil through a suitable resistor and thereby providing a current to the relay coil sufficient to keep the relay switches closed and the lights on.